Templated monolayer polymerization and replication

ABSTRACT

A self-replicating monolayer system employing polymerization of monomers or nanoparticle ensembles on a defined template provides a method for synthesis of two-dimensional single molecule polymers. Systems of self-replicating monolayers are used as templates for growth of inorganic colloids. A preferred embodiment employs SAM-based replication, wherein an initial monolayer is patterned and used as a template for self-assembly of a second monolayer by molecular recognition. The second monolayer is polymerized in place and the monolayers are separated to form a replicate. Both may then function as templates for monolayer assemblies. A generic self-replicating monomer unit comprises a polymerizable moiety attached by methylene repeats to a recognition element and an ending unit that will not interfere with the chosen recognition chemistry. The recognition element is self-complementary, unless a set of two replicating monomers with compatible cross-linking chemistry is employed. In a two-component replication system utilizing two different kinds of recognition chemistries, the initial template undergoes replication cycles, while maintaining two-dimensional segregation of the two types of monomers. During subsequent replications, the component domains experience little or no mixing, allowing the two-component, patterned assembly to be exponentially replicated. After replication, selective mineralization and/or electroless plating may produce a two-dimensional inorganic sheet having patterned domains within it.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/621,897, filed Jul. 17, 2003, now U.S. Pat. No. 7,311,943,which claims the benefit of U.S. Provisional Application Ser. No.60/396,486, filed Jul. 17, 2002, the entire disclosures of which areeach herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to monolayer polymerization and, in particular,to self-replicating systems of monolayers and methods for polymerizingorganic thin film monolayer assemblies.

BACKGROUND

As nanotechnology pushes forward, the need increases for reliablemethods of producing discrete nanostructures, either organic orinorganic, of specific shape and size, particularly in the 2-1000 nmregime. Two general approaches exist for making nanostructures: from thebottom up through chemical synthesis and from the top down throughlithographic methodology. Techniques that target the region between thecurrent capabilities of these two technologies, i.e., from about 2 nm toabout 1000 nm, are currently highly sought after.

Prior art nanostructure synthesis methods that have been developedinclude focused-ion beam milling, scanning probe techniques, and x-raylithography. While advanced mask-based lithography techniques arecapable of producing large quantities of structures of small size, theyare typically very expensive. Although milling techniques and scanningprobe techniques are somewhat more affordable, they are primarily usefulfor the production of very small numbers of nanostructures. Further, allthese available techniques are generally deployed to produce structuresthat are directly attached to surfaces or are integral parts of asurface. There are no general methods to produce mole quantity (6×10²³)amounts of nanostructures that are lithographically defined. Such largequantities of nanostructures are almost by necessity solution based,since they would otherwise occupy a very large amount of surface area.

Biological systems utilize templated replication to produce largequantities of nanostructures such as nucleotide chains and peptidechains. Nucleotide synthesis is based upon hydrogen bond templating,followed by polymerization. Attempts have therefore been made to mimicthe efficiency of oligonucleotide synthesis for various kinds ofpolymers, typically via hydrogen-bonded assembly or electrostaticassembly.

In general, polymerization of monolayers has been extensively studied.Many different routes to achieve non-patterned polymerization of asingle monolayer have been investigated. Of particular relevance arepolymerization systems that are topochemical in nature. A topochemicalpolymerization typically results in very little rearrangement of themonolayer once polymerization has occurred.

The poly(diacetylene)s (PDAs) exemplify such a system. PDApolymerization in both a self-assembled monolayer and in aLangmuir-Blodgett (LB) monolayer on gold has been achieved. FIG. 1depicts a prior art scheme of diacetylene polymerization on a goldsubstrate by attachment of functionalized alkyl thiols. Attempts havebeen made to use hydrogen bonding to control polymerization inLangmuir-Blodgett monolayers. Since PDAs are polymerized by UV light,extensions to lithographic production of monolayers are relativelystraightforward.

PDAs have also been polymerized in covalently bonded multilayers ofmonolayers. A multilayer film can be produced by covalent linkages, withthe number of layers being controlled by a sequence of steps. Multilayerfilms have also been generated using hydrogen bonding and coordinationbonding. FIG. 2 depicts a prior art approach to synthesis of amultilayer film, wherein a second monolayer is grown on a gold-alkylthiol self-assembled monolayer (SAM) via hydrogen bonding (amiderecognition).

Replication of siloxane monolayers through several generations on asubstrate has also been reported. The monolayers replicate through whatis understood to be an acetone-assisted process, involving hydrogenbonding and solvent intercalation for separating the replicate from thetemplate. The replication process is not a one-pot process, nor are themonolayers specifically cross-linked or patterned. The monolayers areattached to the surface of a silicon substrate, and replication stallsafter 4-5 generations. A method of replicating monolayers that is highlycontrolled and can be used to replicate patterns over many generationswould be highly desirable and has never been reported.

Large scale two-dimensional polymers have often been produced byLangmuir-Blodgett techniques (Palacin et al., Thin Films 20:69-82(1995)). One instance of patterned polymer multilayers that are free ofa surface has been reported (Stroock et al., Langmuir 19(6): 2466-2472(2003)), however, synthesis of two-dimensional lithographically definedsingle molecule polymers that can be readily suspended in a solvent hasnot.

Electroless plating of metals onto organic molecules is a commontechnique in biology, often used for histology staining. Electrolessplating onto nanostructures has also been reported recently, using anamide template to coordinate metal ions as the electroless plating seeds(Matsui et al., J. Phys. Chem. B 104: 9576-79 (2000)). In addition,mineralization of organic structures is also a burgeoning field, andtechniques for mineralizing CaCO₃ and SiO₂ are being developed andexplored. Templating of semiconductor crystals has also been reported(Whaley S. R. et al., Nature 405: 665-668 (2000)).

Polymerization of nanoparticles has been reported in many ways.Typically, nanoparticles have been polymerized by using a polymerizablemoiety in the ligand sphere of the nanoparticle (Boal et al., Adv.Functional Mat. 11(6): 461-465 (2001)), or by decorating a pre-existingpolymer chain with nanoparticles (Walker et al., J. Amer. Chem. Soc.123: 3846-3847 (2001)). Polymerization in films has been reported usingdithiol chemistry (Musick et al., Chem. Mater. 12: 2869-2881 (2000)).Further, melting or agglomeration of nanoparticles into films is wellknown (U.S. Pat. No. 6,294,401, Ridley et al. (2001)). However,polymerization of a nanoparticle ensemble using a lithographicallydefined template has not been reported.

What has been needed, therefore, are techniques for making largequantities of nanostructures that target the region between thecapabilities of current technology, i.e., from about 2 nm to about 1000nm. In particular, what is needed is a method for synthesis oftwo-dimensional lithographically-defined single molecule polymers thatcan be readily suspended in a solvent, and may be further used togenerate inorganic structures. What is further particularly needed is amethod of replicating monolayers that is highly controlled and can beused to replicate patterns over many generations, preferably as a“one-pot” process producing monolayers that are specificallycross-linked or patterned.

SUMMARY

These and other objectives are met by the present invention, whichcombines monolayer replication, hydrogen-bonding, and topochemicalpolymerization in order to achieve a self-replicating monolayer system.The present invention features techniques that are particularly usefulfor the synthesis of nanostructures sized from about 2 nm to about 1000nm. The method of the present invention is highly controllable, can beused to replicate patterns over many generations, and is a “one-pot”process producing monolayers that are specifically cross-linked orpatterned. In one aspect, the apparatus and method of the presentinvention provide a self-replicating monolayer system throughpolymerization of a nanoparticle ensemble using alithographically-defined template. The present invention furtherprovides a method for synthesis of two-dimensionallithographically-defined single molecule polymers that can be readilysuspended in a solvent.

The self-replicating system of the present invention may be implementedusing lithography or other techniques known in the art. Once created,the monolayers are used as templates for the growth of inorganiccolloids, such as colloids of metals, semiconductors, and insulators. Inone aspect, the invention features systems of self-replicatingmonolayers. The systems include a group of components, each of which maybe varied, with the combination of the components providing theself-replicating system.

A preferred embodiment of the present invention is a self-assemblingmonolayer (SAM)-based replication scheme. An initial monolayer ispatterned and then used as a template for the self-assembly of a secondmonolayer by molecular recognition. The initial monolayer may optionallybe polymerized, in order to provide better lattice matching andstructural rigidity of the desired pattern. Once the second monolayerhas formed through self-assembly, it is polymerized in place. The twomonolayers are then separated through any suitable mechanism, forming areplicate of the original monolayer. Both the replicate and the originalmonolayer may now function as templates for monolayer assemblies, andthe process can be repeated, forming an exponential replication system.

In a generic self-replicating monomer unit according to one embodimentof the present invention, an ending unit that will not interfere withthe chosen recognition chemistry is attached by methylene repeats to apolymerizable moiety. The polymerizable moiety may be a singlepolymerizable unit, but preferably contains two polymerizable unitsseparated by some number of methylenes. The polymerizable moiety is thenattached by further methylene repeats to recognition chemistry based onany suitable chemistry. Whatever the choice for recognition chemistry,the template must display a complementary recognition element.

The recognition element must be self-complementary, unless there is aset of two replicating monomers. In an exemplary two-componentreplication system utilizing two different kinds of recognitionchemistries, the initial template undergoes replication cycles, whilemaintaining the two-dimensional segregation of the two types ofreplicating monomers having compatible cross-linking chemistry. Duringsubsequent replications, the component domains experience little or nomixing, allowing the two-component, patterned assembly to beexponentially replicated. After replication, selective mineralizationand/or electroless plating may produce a two-dimensional inorganic sheethaving patterned domains within it. In general, inorganic colloid growthmay be achieved through appropriate reduction chemistry of the desiredmetal salts and the use of seed or template-mediated nucleation.

More than two chemically compatible molecules may be used in monolayersynthesis. Patterning of the initial template is accomplished accordingto the defined regions of the two or more molecules composing themonolayer. After replication is complete, the two component replicatesmay then be mineralized or electroless plated in a way that maintainsthe pattern of the replicants, creating opportunities for makingtwo-component inorganic colloids that are patterned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts prior art diacetylene polymerization on a gold substrateby attachment of functionalized alkyl thiols;

FIG. 2 depicts a prior art approach to synthesis of a multilayer film,wherein a second monolayer is grown on a gold-alkyl thiol self-assembledmonolayer via hydrogen bonding;

FIG. 3A illustrates the first part of a self-assembling monolayer(SAM)-based replication scheme according to an embodiment of the presentinvention;

FIG. 3B illustrates the second part of a self-assembling monolayer(SAM)-based replication scheme according to an embodiment of the presentinvention;

FIG. 4 depicts exemplary molecules that can be used in a SAM-basedsystem according to an embodiment of the present invention;

FIG. 5A depicts a generic self-replicating monomer unit utilized in anembodiment of the present invention;

FIG. 5B illustrates a two-component replication system according to anembodiment of the present invention;

FIGS. 6A-B depict generalized replicating monomer units assembling on atemplate according to an embodiment of the present invention;

FIGS. 7A-B illustrate two-component nanoparticle cross-linking andreplication according to an embodiment of the present invention;

FIG. 8 illustrates surface pattern recognition with nanoparticlesaccording to an embodiment of the present invention; and

FIG. 9 depicts synthesis of a BisDA replicating monomer according to anembodiment of the present invention.

DETAILED DESCRIPTION

The present invention combines monolayer replication, hydrogen bonding,and topochemical polymerization in order to achieve a self-replicatingmonolayer system. The self-replicating system can be implemented usinglithography or any other suitable technique known in the art. Oncecreated, the monolayers are used as templates for the growth ofinorganic colloids, such as colloids of metals, semiconductors, andinsulators. In one aspect, the invention features systems ofself-replicating monolayers. The systems include a group of components,each of which may be varied. The combination of the components providesthe self-replicating system.

Polymerization. In accordance with the present invention, polymerizationtechniques are utilized to effect polymer formation in the monolayer. Atopochemical polymerization is typically preferred, although anon-topochemical polymerization may also be advantageously employed. Atopochemical polymerization is preferable because it will generallycause the least perturbation of the monolayer conformation, either on asurface or in a solution. Also, a topochemical polymerization generallydoes not result in polymer formation by solution species, which can beimportant when a system is to be replicated many times.

Polymerizations by externally controllable means relative to thereaction mixture are preferred. Preferably, no additional reagents areused to cause polymerization. Particularly suitable polymerizationmethods include, but are not limited to, ‘reagentless’ polymerizations,such as where a polymerization reaction is catalyzed by heat, byelectromagnetic radiation, or by particle radiation.

A two-dimensional, cross-linked polymer network is generally preferred,and can be produced from monomers with two or more reactive sites. Suchcross-linked monolayers have been made using Langmuir-Blodgett (LB)monolayer techniques (Ahmed et al., Thin Solid Films 187: 141-153(1990)). A cross-linked monolayer is typically more structurally robust.

The polymerization reactions and replication steps are typically carriedout in a solvent. The solvent used to carry out replication is generallyselected for its ability to solubilize the monolayer assemblies and themonomer feedstock.

Monomers and Monolayer. The “monolayer basis” is the base monolayersystem used to form patterns and serves as the initial template forreplication. Monolayers can be formed as self-assembled monolayers(SAMs) on substrates (e.g., ultraflat surfaces), or as LB monolayers at,for example, the air-water interface.

Preferably, the monolayer template is created with as few defects aspossible, making it as close to atomically smooth as possible. Themonolayer basis should be patternable by one of the methods known in theart for two-dimensional patterning. Both SAMs and LB monolayers can beused. LB monolayers are readily prepared in atomically flat form, andmaintain high ordering even during transfer to a substrate. SAM systemson gold typically exhibit a measurable roughness, even on ultraflat goldsubstrates, which may be due to the act of SAM creation itself in thegold/alkyl thiol system. However, small step heights on a surface oftendo not affect the chosen polymerization technique. Siloxane monolayerscan also be prepared on ultraflat surfaces such as glass and silicon.

The monolayer basis, if it has an underlying set of lattice constants,should match the lattice constants and geometries required for themonolayer templating chemistry and the polymerization chemistry. Inaddition, the polymerization employed should result in a polymer withthe requisite lattice constants and angles needed for formation ofanother monolayer after polymerization. For example, in a PDA system,the lattice spacing between monomers is about 4.9 angstroms in order forpolymerization to occur. This lattice spacing should coincide with thelattice spacing necessary for monolayer packing on a SAM or in a LBfilm, as well as with the molecular recognition chemistry needed toassemble a multilayer film. In order for the system of the invention tosuccessfully function as a self-replicating monolayer system, all thesefactors must be considered during selection of the ensemble ofcomponents.

The monomers used to form the replicating monolayers normallyincorporate all the structural moieties necessary to effect the desiredpolymerization technique and/or monolayer formation technique, as wellas to influence such properties as overall solubilities, dissociationmethods, and lithographic methods. Many monomers can be designed for usein templated monolayer replication systems. The monomers typicallycontain at least one, and preferably two, reactive functional groups.The monomers also may contain a terminus bearing one or more molecularrecognition elements, such as, but not limited to, carbonylfunctionalities, heterocycles, and charged moieties. This terminus isused to guide assembly of the second monolayer prior to replication bypolymerization. The monomers can also be designed to enhance colloidalsolubility of the resulting monolayers.

The molecules used to form organic monolayers generally include variousorganic functional groups interspersed with chains of methylene groups.The molecules are typically long chain carbon structures containingmethylene chains to facilitate packing. The packing between methylenegroups allows weak Van der Waals bonding to occur, enhancing thestability of the films produced and counteracting the entropic penaltiesassociated with forming an ordered phase. In addition, hydrogen-bondingmoieties may be present at one terminus of the molecules, in order toallow templating of an adjacent monolayer, in which case thepolymerizable chemical moieties are then placed in the middle of thechain or at the opposite terminus.

As shown in FIGS. 3A and 3B, if a SAM-based system is used, anadditional molecule is generally utilized to form the initial template.This additional molecule has appropriate functionality at one of itstermini in order to form a SAM. For example, on a gold surface, aterminal thiol can be included. There are a wide variety of organicmolecules that may be employed to effect replication. Topochemicallypolymerizable moieties, such as dienes and diacetylenes, areparticularly desirable as the polymerizing components. These can beinterspersed with variable lengths of methylene linkers. Exemplarytarget molecules that can be used in a SAM-based system are shown inFIG. 4. FIG. 5A depicts a generic organic monolayer replicating monomer.

For an LB monolayer system, only one monomer molecule is needed becausethe molecular recognition moiety can also serve as the polar functionalgroup for LB formation purposes. Lithography can be carried out on a LBmonolayer transferred to a substrate, or directly in the trough. Forexample, an LB monolayer of diacetylene monomers can be patterned by UVexposure through a mask or by electron beam patterning.

Monolayer formation can be facilitated by utilizing molecules thatundergo a topochemical polymerization in the monolayer phase, but not inthe solution or gas phase. By exposing the assembling film to apolymerization catalyst, the film can be grown in situ, and changed froma dynamic molecular assembly to a more robust polymerized assembly.

Since polymerization only occurs in the monolayer, monolayer formationcan be promoted by exposure to UV light or polymerization catalysts. Theinherent stresses and surface tensions of thin (1-10 nm) two-dimensionalpolymer or inorganic films can be used to create three-dimensionalfolded structures. “Molecular origami” can then be practiced insolution.

Molecular Recognition. Any suitable molecular recognition chemistry canbe used in forming the assembly. Multilayers have been successfullyassembled based on electrostatic interaction, Van der Waals interaction,metal chelation, coordination bonding (i.e., Lewis acid/baseinteractions), ionic bonding, covalent bonding, and hydrogen bonding.The molecular recognition chemistry used preferably will have spatialrequirements compatible with the polymerization technique employed. Thestrength of the interactions used to assemble the replicate moleculesonto the template monolayer is preferably tuned both for optimalassembly (i.e., low defect density) and for convenient release of thereplicate from the template.

Hydrogen bonding offers a straightforward approach. No discrete bondforming steps are needed, and dissociation of hydrogen-bonded networksmay be caused by thermally heating them to disrupt the hydrogen bonds.Multilayer film assembly in accordance herewith may use hydrogen bondingof amides, carboxylic acids, and amines. Conveniently, the latticeconstants of amide-containing films overlap with the lattice constantsneeded for diacetylene polymerization. Readily reversiblecovalent/coordination bonds, such as disulfides or metal chelatedensembles, may alternatively be used, with reversibility being effectedby oxidation/reduction chemistry. Electrostatic/ionic bonding can alsobe reversibly controlled by protonation-deprotonation reactions.Multilayer films can advantageously be built up by carboxylate-aminechemistries.

Dissociation. A variety of techniques may be employed to effect thedissociation of the replicate monolayer from the template monolayer.Controllable dissociation of the replicated monolayer from the templatemonolayer is preferred. Suitable dissociation mechanisms include, butare not limited to, heat (e.g., similar to DNA denaturation),sonication, irradiation, oxidation/reduction (e.g., electrochemical andreagent chemistries), pH modification, solvent exchanges (e.g., solventpolarity modification), and/or physical separation methods.

In addition, a mild “one-pot” procedure is preferred, particularly aone-pot reaction that allows the entire replicating system to bereplicated many times. Controls that do not require solvent removal orreaction work-up are also preferred, such as, but not limited to,lightwave irradiation, heating, sonication, electrochemical oxidationreduction, addition of monomer feedstock for the replication, andaddition of acids or bases. Preferably, these controls are arranged sothat the system can perform many replications.

As an example, a method of assembling multilayer films in one pot usinghydrogen bonded assembly chemistry is simple, cost effective, and allowsfor the control of overall film thickness and robustness by altering thehydrogen-bonding moieties, alkyl chain lengths, and solutionconcentrations during the film formation step. Preferred methods forseparating the replicate from the template in a hydrogen-bonded systeminclude, but are not limited to, the use of heat, sonication, radiation,and/or solvent exchange. For example, a change in solvent polarity canbe used to disrupt hydrogen bonds.

Other suitable methods of separating the replicate from the template,albeit typically less desirable, include physical stripping from asurface-fixed template. In systems involving covalent bonding betweenreplicate and template (e.g., via disulfides or metal coordinationbonds), oxidation-reduction chemistry can be used, either in anelectrochemical fashion or by direct chemical oxidants/reductants. Insystems involving ionic/electrostatic bonding, pH can be used as acontrol for splitting the replicate and template. Other methods that areused for microstructure manipulations, such as the placement of releaseholes within the two-dimensional structure, may also be used tofacilitate the dissociation of the template from the replicate. Inparticular, release holes allow solvent to access interior locationswithin the structure, thereby increasing the likelihood of splitting twoflat sheets.

Monolayer Patterning. Any of the techniques known in the art formonolayer patterning may be used for patterning of the initialmonolayer. Techniques useful in patterning a monolayer include, but arenot limited to, photolithography, e-beam techniques, focused ion-beamtechniques, and soft lithography. Various protection schemes such asphotoresist can be used for a SAM-based system. Likewise, blockcopolymer patterns can be formed on gold and selectively etched to formpatterns. For a two-component system, patterning can also be achievedwith readily available techniques.

Soft lithography techniques are especially convenient. Ultraviolet lightand a mask can be used for patterning the monomers in place, after theirassembly into a monolayer. For instance, an unpatterned base monolayermay be used as a platform for assembly of the UV/particle beam reactivemonomer monolayer. The monomer monolayer may then be patterned by UVphotolithography, e-beam lithography, or ion beam lithography, eventhough the base SAM is not patterned.

Inorganics. The present invention also allows templating of inorganicstructures using replicated monolayers. Growth of inorganic colloids canbe achieved by various growth mechanisms available for templatedformation of inorganics on organic surfaces, such as through appropriatereduction chemistry of the desired metal salts and the use of seed ortemplate-mediated nucleation. Using the recognition elements thatprovide for assembly of a second monolayer on the first, inorganicgrowth can be catalyzed at this interface by a variety of methods.Colloidally soluble inorganic structures can also be produced.Insulators, semiconductors, and metals, are templatable using eitherelectroless plating techniques or mineralization.

Once the patterned monolayers have been made and replicated as manytimes as desired, the monolayers can be used as templates for the growthof inorganic compounds in the form of colloids bearing the shape of thepatterned organic monolayer. Insulators can be patterned by carbonylfunctionalities; it is well known that calcium carbonate and silica aretemplated by various carbonyl functionalities such as carboxylic acidsand amides. By controlling the crystal growth conditions, it is possibleto control the thickness and crystal morphology of the mineral growth.Titanium dioxide can also be templated.

Templated electroless plating techniques can be used to synthesizemetals using existing organic functional groups. In particular, bychelating metal atoms to the carbonyl moieties of the organicreplicates, electroless metal deposition can be catalyzed on theseorganic replicates, forming patterned metallic colloids. For instance,Cu, Au, Ni, Ag, Pd, Pt and many other metals plateable by electrolessplating conditions may be used to form two-dimensional metal colloids inthe shape of the organic monolayer that has been replicated. Bycontrolling the electroless plating conditions, it is possible tocontrol the thickness of the plated metal layer. If nanoparticles areattached to the hydrogen-bonding surface, such as, for example,covalently by chemical modification, an inorganic solid can be formed bymelting the nanoparticles together. By controlling the size andthickness of the nanoparticle layer, the thickness of the sintered metallayer can be controlled. Likewise, by attaching seed nanoparticles tothe organic template by hydrogen bonding, these seeds can be used ascatalysts for electroless plating onto the organic template.

Carbonyl moieties may be used for templating of semiconducting materialsas well, forming semiconducting colloids based on the shape of theorganic replicant monolayers. Semiconductors of the II-VI type (CdSe,ZnO, and the rest of the analogs) have been reported (Saito et al., Adv.Mater. 14(6): 418-421 (2002)), and III-V semiconductors are alsofeasible, using mineralization, electroless plating, or seed mediatedgrowth.

One major benefit of the method of the present invention is that thereplicated monolayers are used as templates for inorganic structures.Additionally, by using two compatible recognition chemistries within thesame monolayer, such as an amide and a carboxylic acid moiety, thegrowth of separate inorganic compounds and structures can be templatedin whatever pattern was defined on the starting template.

Assaying a replicating organic monolayer system is a difficult task.Techniques that are suitable for assaying small quantities of shapesinclude AFM or cryo-TEM techniques. Growth of inorganic colloids usingthe organic monolayers as templates can also be a useful assaytechnique, allowing for a relatively straightforward examination ofsmall evaporated aliquots of solution by, for instance, SEM, relying ona metal colloid to show up clearly by SEM. Metal colloids grown onorganic monolayers also provide a better spectroscopic handle at thevery low concentrations that are likely to be encountered during theearly replication cycles.

Indeed, specific shapes of replicating organic monolayers, when‘developed’ with a metal, can be expected to have distinct spectroscopicsignatures in the UV-vis or infrared regions due to plasmon bands. Forinstance, colloidal silver triangles have different spectra depending ontheir size and quality. Such distinctive spectroscopic signatures can beused to ascertain the quality and fidelity of the replicating monolayersystem, thus allowing for process optimization during replication.

In addition to replication of monolayers in solution, replication ofpatterned monolayers may also be conducted on a surface. Multilayerfilms involving insulating or semiconducting layers can be produced.Particularly, the assembly of multilayer hydrogen-bonded films of acontrollable thickness can be achieved in a one-step process. Bycontrolling the concentration of a difunctional long-chain alkylmolecule with termini that include hydrogen-bonding groups, multilayerfilms can be produced, the thickness of which depend on theconcentration of the solution. If this approach is combined with aremotely polymerizable (UV initiated for instance) moiety in thecomponent molecules, the resulting film so produced will generally bemore robust than previous one-step methods (Miura et al., Thin SolidFilms 393: 59-65 (2001); Viana et al., Phys. Chem. Chem. Phys. 3:3411-3419 (2001)). In addition, a greater range of thicknesses (numberof multilayers) should be possible.

Additionally, topochemical polymerization can aid in the monolayerassembly process itself. Since polymerization only occurs in themonolayer, monolayer formation can be triggered and promoted by exposureto UV light or polymerization catalysts. Hence, the process of monolayerformation may be kinetically speeded up since the reverse reaction(dissociation of monomer from the monolayer) is not possible once themonomer molecule has been added to a growing polymer chain. By thismethod, the formation of thick multilayers through hydrogen bondinginteractions is made possible.

An example of the system of the present invention is illustrated inFIGS. 3A and 3B, which depict the parts of a SAM-based replicationscheme. As shown in FIG. 3A, an initial monolayer 302, is patterned by achosen technique. In the example of FIG. 3A, a thiol chain is patterned304 on patterned gold film 304 to form a SAM 302 with amide caps 308.Initial monolayer 302 is then used as a template for the self-assembly309 of a second monolayer 310 on top of it by molecular recognition. Theinitial monolayer 302 may itself be optionally polymerized 312, in orderto provide better lattice matching and structural rigidity of thedesired pattern. In the example shown, self-assembly step 309 isinitiated by addition of a PDA precursor chain with amide cap.

Once the second monolayer 310 has formed through self-assembly, it ispolymerized 316 in place. The two monolayers are then separated 318through any suitable mechanism, such as solvent exchange or heat, toform replicate 320 of the original monolayer 302. Both replicate 320 andthe original monolayer 302 can now function as templates for monolayerassemblies 330, 332. As depicted in FIG. 3B, the process can be repeatedmany times, forming an exponential replication system.

A preferred embodiment of the example system illustrated in FIGS. 3A and3B utilizes diacetylene polymerization. The lattice constantsappropriate for the polymerization, the amide hydrogen bonding spacerequirements, and the thiol-gold contact spacing all fall withinessentially the same range, which is preferred. Thus, the spatialrequirements of the polymerization reaction and molecular interactions(e.g., hydrogen bonding, electrostatic or covalent interactions)overlap. For a Langmuir-Blodgett-based system, there is no issue withthe underlying substrate, which also needs to be lattice matched.

FIG. 4 depicts exemplary target molecules (in this case, for C9 chains)designed for use in the system illustrated in FIGS. 3A and 3B. Ingeneral, the number of methylene linker carbons 402 used as spacersbetween the polymerizable moieties 410 and the recognition elements 420can be quite varied, being typically in (but not limited to) a range of1 to 20. Thus, in the exemplary molecules of FIG. 4, any entity labeled“C” followed by a number (referring to the number of methylene units)may be varied in order to construct different target molecules suitablefor use in the present invention.

Molecules 401, 441, 451, 461 are intended to be used for the formationof a patterned template SAM on a gold surface, and allow for the use ofeither amide or carboxylate hydrogen bonding as the organizing principlefor templated replication. In particular, molecules 401, 441 incorporatea polymerizable diacetylene unit, which may be beneficial in locking inthe desired lattice constants and ordering within the base SAM template.However, molecules 451, 461 may work just as well for the formation of abase SAM patterned template, and polymerization is not required. Endingunit 430 will be bound to the gold surface in a SAM, and will notinterfere with the monolayer templating effect.

Molecules 411, 421, 431 are potential replicating monomers. Molecules421, 431 have two polymerizable units 410 in the chain, allowing forthorough cross-linking of the monolayer. The family of replicatingmonomers exemplified by molecule 431(Hentriaconta-11,13,20,22-tetraynoic acid) and by molecule 421(Hentriaconta-11,13,20,22-tetraynoic acid amide) is particularlydesirable for this invention. Also useful areTriaconta-10,12,19,21-tetraynoic acid amide andTriaconta-10,12,19,21-tetraynoic acid. A family of molecules which areespecially useful for the invention is therefore defined as molecules ofthe type of molecule 431 (Hentriaconta-11,13,20,22-tetraynoic acid) ormolecule 421 (Hentriaconta-11,13,20,22-tetraynoic acid amide), whichhave two diacetylene units linked by a methylene chain of from 1 to 20carbons to form a bis(diacetylene) unit, and which have an alkyl chainof from 1 to 20 carbons terminating in an inert functionality such as amethyl on one end of the bis(diacetylene) unit, and which have an alkylchain of from 1 to 20 carbons terminating in an amide or carboxylic acidat the other end of the bis(diacetylene) unit.

While in the embodiment shown molecular recognition between monolayersis achieved by the bonding between amide functionalities or the bondingbetween carboxylic acid functionalities, many other functionalities maybe advantageously utilized in the present invention. Certain othersuitable functionalities may require additional components and/oradditional steps in the replication process that are apparent to one ofskill in the art.

FIG. 5A depicts a generic self-replicating monomer unit, of which themolecules in FIG. 4 are specific examples. In FIG. 5A, ending unit Z 502for the monomer chain may be -methyl, a functionality designed to affectthe solubility of the monomer or resulting colloidal shape (such as, forexample, —CH₂OH), —CH₂OBn, —NMe₂, or any other group that will notinterfere with the recognition chemistry. Ending unit Z 502 is attachedby methylene repeats m 504 to polymerizable moiety Polym 510.Polymerizable moiety Polym 510 may be a single polymerizable unit, butpreferably contains two polymerizable units separated by some number ofmethylenes. Polymerizable units such as diacetylenes, olefins, or dienesare particularly suitable.

Polymerizable moiety Polym 510 is further attached by methylene repeatsn 514 to recognition chemistry Recog 520. Methylene repeats m 504, n 514are used for increasing order and van der Waals interactions in a SAM.Recognition chemistry Recog 520 may be based on any suitable chemistry,including, but not limited to, hydrogen bonding, such as amide-amidebonding, or more complex hydrogen-bonding patterns, such as barbituricacid or diaminotriazine. Whatever the choice for recognition chemistryRecog 520, the template must display a complementary recognitionelement. The recognition element must be self-complementary unless thereis a set of two replicating monomers.

FIG. 5B depicts an exemplary two-component replication system utilizingtwo different kinds of recognition chemistries (i.e., the monolayer iscomposed of two chemically compatible molecules). In FIG. 5B, initialtemplate monolayer 550 containing component A, which contains a patternof component B 551 within it, undergoes replication cycles 555,maintaining the two-dimensional segregation of replicating monomers 560,561 (for two different types of replicating monomer units withcompatible cross-linking chemistry). After replication, selectivemineralization and/or electroless plating 565 produces a two-dimensionalinorganic sheet 570 with patterned domains 575 within it.

One suitable system utilizes two different recognition chemistries inthe diacetylene system, amide-based and carboxylic acid-based. Sincethese systems have very similar lattice constants, they can form thebasis of a self-replicating system composed of two components. Duringsubsequent replications, the carboxylic acid domains and the amidedomains experience little or no mixing, allowing the two-component,patterned assembly to be exponentially replicated. Use of a metal ion tochelate to the carboxylate moiety may be useful in keeping the twocomponents well segregated during replication cycles, maintaining thepattern integrity within the assembly.

More than two chemically compatible molecules may be used in monolayersynthesis. Patterning of the initial template can occur according to thedefined regions of the two or more molecules composing the monolayer.After replication is complete, the two component replicates can then bemineralized or electroless plated in a way that maintains the pattern ofthe replicants, creating opportunities for making two componentinorganic colloids that are patterned.

An alternate embodiment of the present invention provides a replicatingsystem wherein the replicating monomer is not necessarilyself-complementary. In this case, there is no pattern in the monolayerto be replicated, but there are two types of monolayers in the system,each of which are composed of different monomers. In an exampleimplementation, a monomer with Adenine as the recognition elementforming the basis of a monolayer template (to use DNA as a simpleexample) is paired with another monomer terminating in Thymine (the HBond partner of Adenine in DNA) in order to replicate this monolayer.This provides one template terminating in Adenines, and another oneterminating in Thymines after disassociation. The system of thisembodiment is therefore capable of self-replication, but requires twoseparate monomers present at once (typically in equal amounts).

Replication system based on nanoparticles. The present invention may beextended to replication of two-dimensional assemblies of nanoparticles,an example that is also instructive as to the requirements forreplication of monolayers according to the present invention. The basicrequirements of a replication system based on nanoparticles are depictedin FIGS. 6A-B. The key component of the replicating system isgeneralized replicating monomer unit 610. Choices regarding patterningto form the initial template, as well as the replication cycle, aredetermined at least in part by the make-up of replicating monomer unit610.

As shown in FIGS. 6A-B, monomer unit 610 is built on inorganic ororganic nanoparticle 612 to which multiple Crosslinkers 615 areattached. The number of Crosslinkers 615 attached to nanoparticle 612may vary, but monomer unit 610 should have the ability to cross-linkwith more than 2 adjoining monomer units in the two-dimensional matrix.In addition, monomer unit 610 must incorporate Recognition Element 620capable of binding to template 640 reversibly (yet strongly enough toform a complete monolayer on the template), in order that a replicationcycle can be performed. As multiple replicating monomer units 610assemble on template 640 in the xy plane, it is important that they beable to crosslink 615 in multiple directions and not just form chains.This allows formation of a robust sheet that replicates the pattern.

An additional desirable property of the monomer unit, though notstrictly necessary for replication, is that polymerization of themonomer takes place predominantly when it is bound to the template. Inother words, unproductive polymerization of the replicating monomerunit, such as that which takes place in solution away from the 2-Dtemplate, is desirably minimized, preferably having a very low raterelative to the rate of the desired polymerization reaction that occurswhen the monomer is bound to the template. This eases purification ofthe replicated structures, and makes for more efficient use of thereplicating monomer. Minimization of unwanted polymerization helps tomake the system of the present invention a practical replication system.

Topochemical polymerization is a very useful reaction in this context,because it helps ensure that polymerization occurs exclusively on thesurface where the monomers can form an organized array resembling thesolid state. Groups that perform topochemical polymerization, such asdiacetylenes or butadienes, can thus be used as linkers. However,polymerizations that can be speeded up by many orders of magnitude dueto proximity effects on the template are also useful. These may involvea two-member set of replicating monomer units.

For example, one of the monomers (A) may possess epoxides or otherrelatively electrophilic moieties within the ligand shell of ananoparticle, as seen in FIGS. 7A-B. The other monomer unit (B) thenshould possess nucleophilic moieties within its ligand shell that areexpected to react with monomer (A) upon close proximity. However, suchreaction is normally slow when the two monomers are simply dissolved inthe same solution. Only when they enter a phase involving intimatecontact and close packing (such as occurs within a monolayer) do thesegroups react. There is some precedent for this application within therealm of nanoparticle chemistry, as it is often the case thatnanoparticles are stable in solution but irreversibly agglomerate in thesolid phase (Leff et al., Langmuir 12: 4723-4730 (1996)). Both monomers(A) and (B) contain the same recognition chemistry, and distributeevenly across a template surface, giving on average an ensemble mixtureof (A) and (B) which may form a cross-linked sheet.

FIGS. 7A-B depict an especially robust four-hydrogen bondself-complementary recognition motif that is useful for largereplicating monomers. In FIG. 7A, methylene chains 710 shieldelectrophilic amines 720 from epoxide units 730 while in the solutionphase. As seen in FIG. 7B, once on template 750 with exposed quadruplehydrogen-bonding groups 760, methylene chains 710 intercalate, andamines 720 and epoxides 730 react to create a crosslinked sheet.

Nanoparticles that are monofunctionalized regarding the recognitionelement are important for this type of a self-replicating monolayersystem. If the replicating monomer nanoparticles are notmonofunctionalized with regards to the recognition element, formingmultilayers and/or polymeric chains of the replicating monomers willbecome problematic due to unwanted cross-linking. The patent family ofHainfeld et al (U.S. Pat. No. 5,521,289, Hainfeld et al. (1996); U.S.Pat. No. 6,121,425, Hainfeld et al. (2000)) discloses methods for makingmonofunctionalized nanoparticles that involve HPLC purification andvarious precipitations. Various statistical methods can also beenvisioned for obtaining monofunctionalized nanoparticles (which canotherwise be fully functionalized with the cross-linking ligands). Othersuitable methods for making monofunctionalized nanoparticles aredescribed in co-pending U.S. patent application Ser. No. 10/621,790,(“Nanoparticle chains and preparation thereof”, Jacobson et al., Jul.17, 2003).

FIG. 8 depicts an exemplary embodiment of the method of the presentinvention, achieving replication of a structure patterned on gold. Themethod of FIG. 8 includes forming gold patterns 805 on a surface 810 bypatterning with, for example, photoresist and then exposing theunderlying gold surface. Boundaries 812 formed by photoresist define theshape to be replicated. Thereafter, nanoparticles 815 (formed from Au,Ag, or other elements) are anchored to the patterned gold surface viathiol linkages 820 or some other recognition element. Upon heat curing,the nanoparticles can be melted or sintered together 830, forming asolid sheet replicate 840 of the patterned gold, having a thicknessapproximately half the diameter of starting nanoparticles 815.

Alternatively, solution stable nanoparticles that agglomerate in thesolid phase can be used, so long as they are monofunctionalized with arecognition moiety having reversible binding. This provides a relativelysimple replicating unit. After sintering or agglomeration on the 2-Dtemplate, the replicate is then separated from the surface by thermalenergy or mechanical energy, for instance by heating in a solvent ormechanical stripping. The replicant may then itself be used as atemplate for further replication.

Sintering of nanoparticles is one technique known for producing patternson a surface (Fullam et al., Adv. Mater. 12: 1430-1432 (2000); U.S. Pat.No. 6,294,401, Ridley et al. (2001); Wuelfing et al., Chem. Mater. 13:87-95 (2001)). A variety of capping groups and elemental compositionscan be used to help determine the sintering conditions needed.Nanoparticles also spontaneously “melt” when the capping groups areremoved, so more labile capping groups such as amines on gold may beused to facilitate formation of gold films. A replication system basedon nanoparticle sintering or melting can thus be designed to allowexponential replication.

Further specific examples, embodiments and synthesis methods. Thesynthesis of the BisDA replicating monomer 980 was carried out usingCadiot-Chodkiewics coupling chemistry, as is shown in FIG. 9. TheCadiot-Chodkiewics couplings using amines as solvents were found to befar more effective for these compounds than the traditional reagent set.(Alami et al., Tet. Lett. 37(16): 2763-5 (1996)) Molecule 9101,8-Nonadiyne is commercially available. Molecule 920 1-iodo-1-decyne(Narayana, Rao et al. 1995) has been previously synthesized. Usingcuprous iodide and pyrollidine as solvent, these were coupled to producemolecule 940. Molecule 940 was then lithiated to produce molecule 960.Molecule 960 may then be coupled using cuprous iodide and pyrollidinewith 10-undecynoic acid amide to yield molecule 980. 10-Undecynoic acidamide (Crisp et al., Tetrahedron 53(4): 1505-1522 (1997)) has beenpreviously synthesized as well. The bis(diacetylene) 980 is quite labileto heat and light in the solid state or on silica gel, so it is storedin a methylene chloride solution at liquid nitrogen temperatures. Fullsynthetic details follow. Included is a synthesis of 11-dodecynoic acidamide, which can be substituted in step 970 of FIG. 9 to result in thebis(diacetylene) replicating monomer 421 shown in FIG. 4.

Synthesis of molecule 16-mercaptohexadecanamide, similar in function inthe context of the present invention as molecule 461 of FIG. 4, wasachieved by the method reported by Nuzzo and coworkers (Nuzzo et al., J.Am. Chem. Soc. 112: 558-569 (1990)). This molecule was used to create abase SAM template for replication of monomer 980.

11-dodecynoic acid amide (an alternate chain for building the BisDAreplicating monomer) 421. 11-Dodecyne nitrile (3.936 g, 22.2 mmol) andpotassium carbonate (0.441 g, 3.19 mmol) were added to a flask andinerted with nitrogen, followed by the addition of 6.7 mL of DMSO. Theflask was cooled in an ice bath and 2.7 mL of 30% H₂O₂ was added slowlyvia syringe. The reaction was allowed to warm to room temperature andstirred overnight. Additional hydrogen peroxide can be added if thereaction shows remaining starting material. The reaction was dilutedwith 100 mL of diethyl ether and worked up by extraction with 1 M HCl(3×80 mL), and with water (3×80 mL). The organic phase was dried overMgSO₄ and concentrated in vacuo to yield 2.352 g of pure A. 54% yield;¹H NMR (CDCl₃) δ 5.55 (s, 2H, NH₂), 2.18 (m, 4H, CH₂—C≡C & CH₂—CO), 1.92(t, J=2.4 Hz, 1H, H—C≡C), 1.61 (m, 2H, CH₂—C—CO), 1.49 (m, 2H,CH₂—C—C≡C), 1.26 (m, 10H, CH₂ chains); MS (ESI) [M+Na]⁺ calc. 218.1515found 218.1516. Elemental analysis calc. for C₁₂H₂₁NO: C, 73.80; H,10.84; N, 7.17. Found: C, 74.14; H, 10.99; N, 7.54.

Nonadeca-1,8,10-triyne (940). Pyrollidine (20 mL) and CuI (0.65 g, 3.42mmol) were added to a nitrogen flushed reaction vessel. Nona-1,8-diyne(1.58 g, 13.17 mmol) was added via syringe. 1-Iodo-1decyne (2.26 g, 8.53mmol) was added via syringe dropwise to the solution over ten minutes.The reaction was stirred under nitrogen for 24 h. The reaction mix wasthen quenched with ammonium chloride (10 mL), separated with diethylether, and dried with anhydrous magnesium sulfate.Nonadeca-1,8,10-triyne was then isolated using silica columnchromatography with a 1% ether/hexane eluting solution obtaining 1.06 gof an oil. 50% yield; ¹H NMR (CDCl₃) δ 2.29 (m, 4H, CH₂—C≡C), 2.22 (dt,2H, CH₂—C≡C, J=7, 2.7 Hz), 1.97 (t, 1H, H—C≡C, J=2.7 Hz), 1.54 (m, 6H,CH₂—C—C≡C), 1.33-1.40 (sextuplet, 2H, CH₂—CH₂-CH₃), 1.27 (m, 10H,C—CH₂—C), 0.88 (t, 3H, CH₃); ¹³C NMR (CDCl₃) δ: 84.62, 77.99, 77.36,68.63, 65.76, 65.45, 32.21, 29.54, 29.46, 29.25, 28.72, 28.34, 28.31,28.23, 23.06, 19.61, 19.52, 14.53; MS (ESI) [M+Na]⁺calc. 279.2083 found279.1723 (very unstable to any MS technique). Elemental analysis calc.for C₁₉H₂₈: C, 88.99; H, 11.01. Found: C, 88.80; H, 10.96.

1-Iodo-nonadeca-1,8,10-triyne (960). Nonadeca-1,8,10-triyne (0.802 g,3.133 mmol) and anhydrous THF (96 mL) was cooled to −78° C. in a dryflask under nitrogen. LiN[Si(CH₃)]₂ (LHMDS) in THF (3.76 mmol) was addedto the reaction mix slowly via dry syringe. In a separate flask I₂ (9.55g, 3.76 mmol) was dissolved in dry THF (20 mL). The iodine solution wasadded dropwise to the nonadeca-1,8,10-triyne solution until reactioncompletion (notably becoming orange-red). The reaction was stirred for30 min and slowly warmed to room temperature. The reaction was extractedwith diethyl ether and 1M K₂S₂O₃. The organic phase was dried overanhydrous MgSO₄, and concentrated by evaporation to yield1-iodo-nonadeca-1,8,10-triyne (0.93 g, 2.45 mmol). GC/MS showed nostarting material remaining. 79% yield; ¹H NMR (CDCl₃) δ 2.15-2.33 (m,6H, CH₂—C≡C), 1.48 (m, 6H, CH₂—C—C≡C), 1.33-1.39 (m, 2H, CH₂—CH₂-CH₃),1.28 (m, 10H, C—CH₂—C), 0.85 (t, 3H, CH₃).

Triaconta-10,12,19,21-tetraynoic acid amide (BisDA) (980). CuI (0.126 g,0.66 mmol) and 10-undecynoic acid amide (0.29 g, 1.59 mmol) were addedto a flask and inerted with nitrogen. Pyrollidine (5 mL) was then added.In a separate flask 1-Iodo-nonadeca-1,8,10-triyne (0.5 g, 1.3 mmol) wasmixed with pyrollidine (5 mL) and subsequently added slowly to the amidesolution. The reaction mix was left in darkness under nitrogen for 48hours, then quenched with aqueous 1M NH₄Cl (10 mL), and worked up withCH₂Cl₂ and 1 M HCl. The organic was dried over anhydrous MgSO₄. Organicproducts were concentrated by rotary evaporation, although polymerformed, decreasing yield. Hexanes trituration removed unreacted1-Iodo-nonadeca-1,8,10-triyne. Desired product was obtained by severalcrystallizations from hexanes/ethyl acetate, again under darkconditions. All handling of the solid was done under red light. Finalproduct triaconta-10,12,19,21-tetraynoic acid amide was made up of whitecrystals (0.377 g, 0.86 mmol) and was stored frozen (liquid nitrogen) inmethylene chloride. 65% yield; ¹H NMR (CDCl₃) δ: 5.31 (s, 2H, NH₂),2.22-2.26 (m, 10H, CH₂—C≡C & CH₂—CO), 1.58-1.66 (quin, 2H, J=7,CH₂—C—CO), 1.45-1.56 (m, 8H, CH₂—C—C≡C), 1.28-1.4 (m, 20H, C—CH₂—C),0.86-0.91 (t, 3H, CH₃); ¹³C NMR (CDCl₃) δ 175.69, 77.98, 77.84, 77.34,65.69, 69.45, 65.37, 57.68, 53.63, 38.37, 38.35, 33.80, 32.97, 32.92,32.03, 29.34, 29.27, 29.07, 28.94, 28.55, 28.47, 28.26, 28.26, 28.06,27.17, 25.67, 22.86, 19.39, 19.32 14.30. MS (ESI) [M+H]+calc. 436.3574found 436.3560.

Formation of a patterned monolayer template utilizing amide hydrogenbonding, followed by formation of the first replicate. Patterning andformation of an initial template for replication using the replicatingmonomer triaconta-10,12,19,21-tetraynoic acid amide (BisDA 980) can beperformed as follows. An ultraflat gold substrate is prepared by atemplate stripping technique. The substrate is immediately stamped witha patterned poly(dimethylsiloxane) stamp which has been wet-inked orcontact-inked with octadecanethiol (Libioulle et al., Langmuir 15:300-304 (1999)). After stamping, the substrate is immersed into asolution of 0.1 mM 16-mercaptohexadecanamide in ethanol for 4 hours. Thesubstrate is then transferred to a solution of 0.25 mM BisDA (indecalin, under low light conditions).

The substrate is soaked in the solution of BisDA in darkness for 12-16hours. Upon removal of the substrate, it is blown dry with nitrogen, butnot rinsed. Areas of the substrate exclusively covered with abis(diacetylene) adlayer dewetted. The substrate is then polymerized ina nitrogen atmosphere for 2 minutes using a UV pen lamp at 254 nm,forming a cross-linked replicate of the template pattern. The amount ofUV exposure is important for proper cross-linking of the replicatestructure. Two minutes is at the lower end of the preferred exposuretime, while 60 minutes is at the upper end. In addition, the degree oforder in the patterned template monolayer is critical. The higher thedegree of order, the better the replicate monolayer forms and ispolymerized. The degree of order for both the template monolayer and thereplicate monolayer can be judged by contact angle, ellipsometry, andgrazing angle FTIR among the typical techniques.

The solvent used for formation of the pre-polymerized replicate/templatestructure (often called an adlayer structure in the literature) isimportant. Non-hydrogen bonding solvents are preferred when using theBisDA system. Solvents such as decalin (decahydronapthalene) form thepre-polymerized adlayer structure quite well. Other similar solvents,such as hexadecane and dodecane will also be expected to performsimilarly. In addition, comixtures of decalin and toluene with ratios upto 1:3 decalin:toluene have been found to produce polymerizable adlayerstructures. Other mixtures of solvents that allow for the desiredhydrogen bonding interaction in the case of the BisDA molecule andsimilar molecules are included as possible solvents for use duringreplication cycles.

Using soft lithography, templates with features of many microns down to100 nm are accessible. For very small templated shapes and features, analternate fabrication technique may be needed due to difficulties withalkyl thiol ink diffusion. Also, alkyl thiol ink diffusion may createsome disorder at the edges of a given pattern, decreasing the resolutionof a replicate monolayer. An approach based on an inorganic e-beamresist, such as HSQ, should make it possible to directly fabricate thiolpatterns with very small features on ultraflat gold.

Liftoff or ‘melting’ of the first replicate. The patterned replicatemonolayers are themselves soluble and can be used to begin replicationcycles in solution, away from the patterned surface. For instance, theshapes can be lifted off from the substrate in polar solvents that arecapable of solubilizing the replicate monolayers, which have alkylgroups on one side and amide groups on the other side. The monolayersheets in the case of BisDA are approximately 2.5 nm thick, as judged byellipsometry measurements on a surface. These monolayer sheets may ormay not remain flat when they are solubilized, and their degree ofcurvature and aggregation will be dictated by the solubility parametersof the solvent in which they are dissolved. Appropriate solvents for theshapes include warm chloroform and N-methyl-pyrrolidinone. Furthersolvents with similar solubility characteristics are also appropriatefor solvation, such as, but not limited to, dichloroethane and otherhalogenated solvents, and the large family of dipolar aprotic solventswhich are well known to disrupt hydrogen bonding (for exampledimethylsulfate, hexamethylphosphoramide, dimethylformamide,N,N-dimethyl acetamide). Solvation of replicated monolayer structureswill also depend in large part on the size and shape of the pattern.Larger micron and higher-sized patterns may be more prone to aggregationthat will inhibit further replication cycles. Smaller patterns below 1micron in size will be more soluble and easier to replicate.

Solution replication of monolayer patterned shapes. Replicationchemistry is preferably conducted in fluorinated labware to prevent lossof replicated monolayers due to surface adhesion. In general, thereplication system is kept in darkened conditions to ensure thatunnecessary degradation of the replicating monomers or monolayers doesnot occur. A solvent such as decalin is used for chelation of thereplicating monomers to the template monolayers. The solution is exposedto UV light, 254 nm. In order to separate the replicated monolayer fromthe template monolayer, several options exist depending on the size ofthe replicated shape/pattern. Heating of the decalin solution maysuffice. Addition of more replicating monomer, so that it breaks apartthe two monolayer sheets, may also be useful. Solvent addition in theform of a volatile chlorinated solvent, such as chloroform or methylenechloride, combined with heating, may further be a useful technique. Or acombination of these options may be necessary, again depending on thesize of the replicated pattern. Upon starting the next replicationcycle, removal of any added chlorinated solvent can be accomplished byvacuum evaporation, since decalin has a much lower volatility than asolvent such as chloroform.

Monitoring of replication cycle progress can be assayed in many ways.Since the BisDA monomer forms a polymer sheet with a high absorptioncoefficient in the visible light region, simple UV-vis monitoring may beuseful. In addition, assays based on taking aliquots can be used. Analiquot may be analyzed by AFM (contact, non-contact, tapping, eitherafter drying the aliquot or in the solution phase). Alternatively,cryo-TEM techniques based on a flash freeze and metal evaporation atliquid nitrogen temperatures or mass spectrometry techniques can beused. A technique based on electroless plating or immunogold-silverplating can be used for either TEM or SEM evaluation.

Preparation of Ultraflat Gold Substrates. Ultraflat Template StrippedGold substrates are fabricated using mica from SPI (grade V-4 muscovite)as follows. 150 nm of gold is e-beam evaporated at 2 A°/sec onto freshlycleaved mica, followed by 50 nm of titanium at 2-3 A°/sec, as monitoredby QCM. The e-beam chamber is typically at 3*10⁻⁶ torr, with notemperature control on the substrates. These gold substrates are thencoated with a layer of spin-on-glass to prevent alloying of indium withthe titanium and gold. Filmtronics SOG 20B is applied by staticdispensing, followed by spinning at 2000 rpm for 30 seconds. Thesubstrates are soft-baked at 80, 150, and 250° C. for one minute each.The substrates are then immediately placed upside down onto a glassslide covered with molten indium at 250° C. on a hot plate. For 1.4 cm²mica substrates, a 1 cm² piece of 10 mil thick indium foil is more thanadequate. The mica is pressed firmly down with a hot weight to form anindium/gold/mica sandwich. After 1-2 min, the substrates are set asideto cool, and can be stored until needed. The sandwich can be cleaved byplacing it in hot DI water (80-100 C) for about 10 minutes. Trimming aside of the mica aids this process, thus ensuring that one edge is not‘sealed’ by indium or spin-on-glass. The gold surfaces thus producedhave RMS roughness values of 0.35-0.45 nm as measured by AFM.

The apparatus and method of the present invention, therefore, provide aself-replicating monolayer system. The present invention featurestechniques that may be advantageously employed for making nanostructuresof sizes from about 2 nm to about 1000 nm. The method of the presentinvention is highly controllable, can be used to replicate patterns overmany generations, and is preferably, though not required to be, a“one-pot” process producing monolayers that are specificallycross-linked or patterned. In one particular embodiment, the system ofthe invention utilizes polymerization of a nanoparticle ensemble using alithographically-defined template. Another particular embodiment of thepresent invention provides a method for synthesis of two-dimensionallithographically defined single molecule polymers that can be readilysuspended in a solvent. Each of the various embodiments described abovemay be combined with other described embodiments in order to providemultiple features. Furthermore, while the foregoing describes a numberof separate embodiments of the apparatus and method of the presentinvention, what has been described herein is merely illustrative of theapplication of the principles of the present invention. Otherarrangements, methods, modifications and substitutions by one ofordinary skill in the art are therefore also considered to be within thescope of the present invention, which is not to be limited except by theclaims that follow.

1. A method for replicating a monolayer comprising the steps of: forminga first set of monomers into a first patterned monolayer having adesired pattern; attaching a second set of monomers to the firstpatterned monolayer, forming a second patterned monolayer attached tothe first patterned monolayer; polymerizing the second patternedmonolayer, forming a replicated monolayer attached to the firstpatterned monolayer; and disassociating the replicated monolayer fromthe first patterned monolayer.
 2. The method of claim 1, furthercomprising the step of polymerizing the first patterned monolayer. 3.The method of claim 2 wherein the step of polymerizing the firstpatterned monolayer employs a topochemical polymerization.
 4. The methodof claim 1, wherein the monomers are nucleotides or oligonucleotides. 5.The method of claim 1, wherein the monomers are amino acids.
 6. Themethod of claim 1, wherein the monomers are nanoparticle ensembles. 7.The method of claim 1, wherein the monomers contain at least tworeactive functional groups.
 8. The method of claim 1, wherein themonomers contain a terminus bearing one or more molecular recognitionelements.
 9. The method of claim 1, further including the step ofcreating at least one additional replicated monolayer by utilizing thedisassociated replicated monolayer in place of the first patternedmonolayer in the steps of attaching, polymerizing, and disassociating.10. The method of claim 1, wherein the monomers are selected from thegroup consisting of Hentriaconta-11,13,20,22-tetraynoic acid,Hentriaconta-11,13,20,22-tetraynoic acid amide,Triaconta-10,12,19,21-tetraynoic acid amide, andTriaconta-10,12,19,21-tetraynoic acid.
 11. The method of claim 1,further including the step of selective mineralization of thedisassociated replicated monolayer.
 12. The method of claim 1, furtherincluding the step of electroless plating of the disassociatedreplicated monolayer.
 13. The method of claim 1, further including thesteps of nanoparticle adhesion to, and sintering of, the disassociatedreplicated monolayer.
 14. The method of claim 1, further including thestep of growing an inorganic structure upon the disassociated replicatedmonolayer.
 15. The method of claim 1, wherein the step of polymerizingthe second patterned monolayer employs a topochemical polymerization.